Electromechanical transducers are commonly used in connection with stringed musical instruments, especially with acoustic guitars. U.S. Pat. Nos. 3,073,203 issued to Evans and 3,712,951 issued to Rickard are typical examples of prior art bridge pickups where each string contacts a separate transducer. String contacting transducers usually have a wide frequency response and are usually maximally responsive in the vertical plane; that is, in a plane perpendicular to that of the strings and perpendicular to the plane of the fingerboard of the instrument.
A first problem exists, when a string is stimulated near a string contacting transducer, that any resulting transient is over-emphasized in the pickup signal. A second problem exists when pickups which are maximally responsive in the vertical plane are used in a stringed instrument, that body noises and body resonances are over-emphasized in the pickup signal when the resonating body reacts against a transducer contacting a string. This may lead to acoustic feedback when the instrument is amplified and reproduced through loudspeakers. A third problem exists when such vertically responsive pickups are used in a stringed instrument having a vibrato tailpiece or a tremolo-bridge, that the important changes in the string tension caused by the operation of such devices produce large offsets or spurious vibrations in the transducer signal which are difficult if not impossible to filter out without significantly reducing the sensitivity of the pickup to desirable string vibrations.
It is possible to reverse the polarity of every other string transducer in the pickups of the inventions mentioned earlier, in order to cancel the effects of common body vibrations in the sum of the signals. U.S. Pat. No. 3,137,754 issued to Evans describes such a pickup. U.S. Pat. No. 4,314,495 issued to Baggs and U.S. Pat. No. 4,491,051 issued to Barcus are further examples of bridge pickup designs based on this concept, but none of the above-mentioned pickups produce separate noise-free string signals nor can they be used to reduce the adverse proximity effect caused by nearby string stimulation.
In U.S. Pat. No. 3,137,754 Evans tentatively suggests that an idle transducer located near a string contacting transducer may serve to cancel common body vibrations but this method fails to perform over the required bandwith, especially in the low frequencies where virtually no effect is produced.
U.S. Pat. No. 3,453,920 issued to Scherer describes a noise-cancelling string transducer having minimum sensitivity in the vertical plane. The transducer is quite insensitive to finger and body noises but when such a transducer is used in a fretted instrument such as a guitar, and the transducer signal is reproduced by an amplifier, the sound of the fretted notes is significantly and displeasingly different from the sound of the open strings. This unacceptable tone distortion is mostly noticeable when the vibrating string is displaced laterally on the contacting fret in such instances as bending the string or performing a vibrato. It is generally agreed to in the prior art that a guitar string transducer should have high sensitivity in the vertical plane and preferably in all planes of vibration of the string. This would seem to foreclose the possibility for a string transducer to have a high sensitivity to the desirable string vibrations and minimum sensitivity to undesirable body noises and resonances, to transducer proximity effect and to changes in the string tension.
It is therefore a broad object of the present invention to provide an electromechanical pickup for a stringed instrument capable of monitoring the desirable vibrations of one or more contacting strings while rejecting undesirable vibrations occurring in planes possibly including the plane of the monitored desirable vibrations.
It is a more specific object of the present invention to provide a contact pickup for an instrument string which rejects undesirable bridge vibration frequencies while remaining normally sensitive to the corresponding frequencies in the desirable string vibrations.
It is another object of the present invention to provide a noise-cancelling pickup for use in a guitar or similar instrument having a vibrato tailpiece or a tremolo-bridge.
It is a further object of the present invention to provide a bridge pickup which is less sensitive to nearby string stimulation than prior art devices.
It is a still further object of the present invention to produce this noise-cancelling effect possibly without using signal filtering circuitry.